Bacterial pathogens require iron in order to establish an infection in mammalian hosts. The host sequesters iron in heme (iron-porphyrin) or iron-storage proteins. In response, bacteria have evolved mechanisms to subvert the host's sequestration of iron. Understanding these mechanisms can lead to the development of new anti-infectives that block bacterial iron uptake during infection. B. anthracis is the causative agent of the disease anthrax and a potential weapon of bioterrorism. How Gram-positive bacteria like B. anthracis attain iron for growth in mammals is not known. We have uncovered an iron acquisition system in B. anthracis that uses secreted NEAT (near iron transporter) proteins (hemophores) to extract heme from host hemoglobin. Components of this system are found in several Gram-positive bacteria. Biomedical science continues to progress towards understanding cellular processes in the context of an interconnected network of organ systems, as exemplified by the optical imaging of cancer metastasis. Such technology has not readily been applied to host/pathogen interactions. In this application, we propose to use B. anthracis as a model system to develop an optical imaging platform to study iron acquisition in infected hosts. We hypothesize heme uptake via NEAT hemophores enhances the growth and dissemination of B. anthracis during infection. We also postulate that B. anthracis hemophores function to acquire and deliver host heme to replicating B. anthracis in vivo. These hypotheses will be tested using novel near-infrared (NIR) imaging methods in combination with conventional pathogenesis studies to address the following specific aims: 1.Develop NIR probes that facilitate the visualization of B. anthracis in infected hosts. A genomic reporter (infrared fluorescent protein - IFP) and a soluble NIR-labeled hemophore probe will be developed and their in vitro biological properties characterized. 2. Determine the contribution of hemophore-mediated heme uptake to B. anthracis pathogenesis and heme-assimilation during infection of mammalian hosts. Molecular imaging and conventional pathogenesis studies will be used to characterize hemophore- mediated heme uptake and determine if NEAT hemophores enhance B. anthracis replication, dissemination, and onset of anthrax disease. These studies aim to (i) develop and apply the use of optical imaging to study host/pathogen interactions, (ii) determine the contribution of hemophore-mediated heme-uptake to B. anthracis infection dynamics, and (iii) increase our understanding of bacterial iron uptake systems to aid in the development of new therapeutics to combat infection. PUBLIC HEALTH RELEVANCE: This proposal attempts to apply optical imaging technology to the field of Microbiology to highlight a pathogen's activities during infection. An understanding of the dynamics and mechanisms by which pathogens survive, grow, and spread inside mammalian hosts will provide researchers with new tools to identify targets for drug development. Such therapeutics will be used to combat the growing threat to public health caused by reemerging and weaponized infectious agents.